In the conventional use of photochemical reaction such as optical cleaning, surface modification and sensitization of a chemical substance, an excimer discharge lamp is used as a light source for ultraviolet rays. For example, rare gas such as xenon, and halide such as fluoride are enclosed as gas for light emission of the excimer discharge lamp. The halogen or halide is ionized at time of lamp lighting, so that halogen ions are formed, whereby the reactivity with other substances becomes very high. For this reason, the electric discharge container of the excimer discharge lamp needs to be devised so that the halogen or halide can be enclosed. Moreover, in the use of photochemical reaction, instead of an annular excimer discharge lamp which is often used to process a workpiece having a flat face by irradiation, an excimer discharge lamp which can perform face irradiation is desirable in view of capable of controlling light intensity distribution unevenness. For this reason, it is necessary to devise the electric discharge container of the excimer discharge lamp, so that face irradiation can be performed. An excimer discharge lamp disclosed in, for example, Japanese Patent Application Publication No. 06-310106 is conventionally known to fulfill such conditions.
FIG. 6 is an explanatory diagram of a conventional excimer discharge lamp 100, and is a cross sectional view thereof taken along the central axis of disk-like window members 101. The conventional excimer discharge lamp 100 comprises the window members 101 which consists of a pair of disk like shape plates, a pair of electrodes 102 which are provided on the respective exterior surfaces of the pair of window members 101, a electrical discharge space spacer 109 which is arranged between the pair of window members 101, sealing portion materials 105 respectively provided between the window members 101 and the electrical discharge space spacer 109, a pair of metallic members 106 which are respectively in contact with circumferential end faces of the window members 101, and which hold the window members 101 therebetween, bolts 107 which are inserted in respective through holes which pass through the metallic members 106 and the electrical discharge space spacer 109, and a pair of nuts which are respectively provided in both ends of the bolts 107, and which hold the exterior surfaces of the pair of window members.
In the conventional excimer discharge lamp 100, when the pair of window members 101 is held by the bolts 107 and the nuts, the window members 101 and the electrical discharge space spacer 109 are sealed by the sealing portion materials 105 therebetween. Thus, in the excimer discharge lamp 100, an electrical discharge space 104 is formed by the pair of window members 101, the electrical discharge space spacer 109, and the sealing portion materials 105. In the electrical discharge space 104, rare gas such as krypton (Kr) and xenon (Xe) and halogen such as fluorine (F2) and chlorine (Cl2) are enclosed as gas for light emission.
Since halogen gets in contact with these members which form the electrical discharge space 104, material having low reactivity with halogen is adopted therefore. Specifically, when the window members 101 are made of sapphire (Al2O3) or metal oxides other than silicon, such as single crystal yttria (Y2O3), it is possible to prevent the window members 101 from deteriorating. Moreover, the sealing portion materials 105 are made from O-rings having low reactivity with halogen, such as perfluoroelastomeror or fluorine contained resin.
In the conventional excimer discharge lamp 100, excimer electric discharge is caused in the electrical discharge space 104 by supplying high voltage of high frequency between the pair of electrodes 102. For example, when the gas for light emission consists of krypton and fluorine, ultraviolet rays having a wavelength band of 240 nm-255 nm are obtained. Moreover, when the gas for light emission consists of xenon and chlorine, ultraviolet rays of a wavelength band of 300 nm-320 nm are obtained. The ultraviolet rays produced in the electrical discharge space 104 pass through the window members 101, and are emitted to the outside from the mesh of the electrodes 102 which are made up of a metal net. Since the window members of the excimer discharge lamp 100 are plates, face irradiation can be performed from the exterior surface of the window members, so that a workpiece to be irradiated (not shown), which faces the window members, can be suitably processed.